Thanks :-) https://t.co/tCO9IipruB
When I tried to edit the settings thru "edit settings" on my Microsoft server 2008 R2 templates in vSphere Client version 4.1.0 build 258902 I get the following error:
Call "PropertyCollector.RetrieveContents" for object "propertyCollector" on vCenter Server "name vCenter server" failed.
I removed the VM template from the inventory and added it again from the data store. After this trick it was working again. Problem solved!
But what was the problem? According to Bjorn Bats (http://www.bjornbats.nl) who was incredibly fast with his response it seems that this happens after an upgrade in vSphere. With this conclusion he could be right, because I just updated my vSphere farm from ESX 4.0 Update 2 to ESX 4.1.
It's wise to check if you still can convert en deploy a new virtual server. Just to be sure!